Various types of electric lamps, and particularly halogen incandescent lamps, include a fill gas which has in inert component and an additive. Halogen incandescent lamps have an inert base component and a halogen contaning additive. The quantity of the halogen containing additive in the inert gas is controlled by the vapor pressure.
In a method which has been proposed to enrich a gas with an additive, appropriate dosing of the base gas is obtained by providing the additive in solid or liquid form in a vessel or container which is then brought to a predetermined temperature, causing a certain vapor pressure to arise. This vapor pressure is the one required to enirch the base gas, flowing with a predetermined speed through the vessel, with a predetermined quantity of the additive.
The referenced U.S. Pat. No. 3,788,725 describes a process to fill a halogen incandescent lamp by dosing the halogen concentration of the fill gas by conducting an inert gas through a carbon-bromine, CBr.sub.4 granulate. The container which receives the CBr.sub.4 must be brought to that temperature at which the CBr.sub.4 generates that vapor pressure which is required in order to enrich the inert gas with the appropriate quantity of halogen additive for operation of the lamp.
The type of dosing described in the patent is difficult to control, and the quantity of halogen additive in the inert gas is subject to variations. The mixing container, thus, is connected to an infrared (IR) gas analyzer which continuously measures the halogen concentration in the mixed fill gas and, if the halogen concentration is not at the desired level, it either changes the temperature of the CBr.sub.4 or the flow speed of the inert gas.